The present invention relates to a dry planographic plate having a non-image area constituted by a silicone rubber layer, and more particularly, to a dry planographic plate improved to be able to maintain an excellent ink receptivity by coating the surface thereof with a layer containing an organic polymer. The invention also pertains to a method of preparing the above dry planographic plate, and an organic polymer solution for coating the plate surface with a layer containing an organic polymer, as well as a processing apparatus for coating the plate surface with a layer containing an organic polymer.
As a dry planographic plate having a non-image area constituted by a silicone rubber layer backed with a substrate, for example, the following various plates have been proposed: (A) a plate formed by providing an image-forming substance layer (photosensitive layer), on a substrate and further providing a silicone rubber layer on the image-forming substance layer (i.e., a plate having silicone rubber as the upper layer) as shown in the specifications of U.S. Pat. Nos. 3,894,873 and 4,358,522, for example; (B) a plate formed by providing an image-forming substance layer (photosensitive layer) on a silicone rubber layer backed with a substrate (i.e., a plate having a silicone rubber as the lower layer), as shown in the specifications of U.S. Pat. Nos. 3,677,178, 3,949,142 and 3,909,265, for example; and (C) a plate constituted by only a silicone rubber layer backed with a substrate, the silicone rubber layer itself having photosensitivity so as to form an image (i.e., a plate having only a silicone rubber layer), as shown in the specifications of U.S. Pat. Nos. 3,953,212 and 3,865,588, for example.
These unprocessed dry planographic plates are processed by a known method to obtain dry planographic plates each having a non-image area (ink-repelling area) constituted by the silicone rubber layer. However, in the image area (ink-receiving area) of each of these plates is present a silicone compound which has supposedly oozed out from the adjacent silicone rubber layer, or moved from the non-image area in developing the plate.
Moreover, this silicone compound is apt to concentrate on the surface of the image area. If the plate is stored for a long period of time, the silicone compound concentrating on the image area surface further increases in amount.
Therefore, when printing is effected using a dry planographic plate having a non-image area constituted by a silicone rubber layer, particularly when a dry planographic plate which has been stored for a long period of time after processing is employed, the silicone compound present in its image area (ink-receiving area) impairs the ink receptivity, making it impossible to obtain a good print, disadvantageously.